Phil asks this question, which is about the power supply for LED downlighters and a tripping problem. It has been answered by Megaman (Theme – Lighting):
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Question: An old array of 10 off 12V tungsten downlighters keeps on tripping the mains; another electrician said ‘replace the bulbs with LED’, so the client swopped them with B&Q LEDs (Diall made in China) - GU5.3 4.5W but the supply still tripped.
I investigated: each downlighter had a 50V AC transformer with a primary resistance of 65ohm - no wonder 10 in parallel tripped the 6A breaker!
Easy I thought - power all 10 off 4.5W LEDs off one transformer through the existing black and red wiring and put a warning notice on the consumer unit.
This worked - all 10 LED lamps were bright and there was no tripping. However, client has rung me to say they now go dim after 15 minutes.
So, the question is, do 10 off 4.5W LEDs daisy chained together need a special type of supply?
Answer: You can’t wire 10 lamps in series on one transformer like that as, unfortunately, you will get a volt drop. This is so irrespective of whether you have halogen or LED lamps.
The issue appears to be surges from the MCB. This could have probably been solved by replacing the transformers for a compatible and approved driver for the lamp.
Alternatively, you could alter the wiring and change to mains voltage GU10s.
If you want to stick with ELV, then when you install the new transformers / drivers (one lamp to one driver) you should replace with new lamp holders and tails for a good connection, as lamp holders and tails deteriorate over time through heat and oxidation.
I recommend that you hire a qualified and / or competent person to investigate further.
When halogen lamps fail it is common that the moment of failure was induced by a momentary surge in current, which could cause tripping of the MCB.
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